1. Field of the Invention
Aspects of the present invention relate to a battery pack, and more particularly, to a battery pack which can prevent the displacement of a protection circuit board and visual defects, and thus, enhance stability.
2. Description of the Related Art
Secondary batteries are more economical than disposable batteries, because they can be repeatedly charged and discharged. Also, secondary batteries can realize a high capacity in a small volume, and thus, can be widely used in portable electronic/electrical devices, i.e., mobile phones, camcorders, or notebook computers, as a power source.
Such secondary batteries include, for example, nickel-cadmium batteries, nickel-hydride batteries, nickel-zinc batteries, and lithium secondary batteries. Among theses batteries, the lithium secondary batteries are the most widely used, because of their small size, high capacity, high operating voltage, and high energy density per unit weight.
A lithium secondary battery may be classified as can-type or pouch-type, depending on the shape of a casing accommodating an electrode assembly. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The can-type batteries may be further classified as cylindrical or prismatic.
In the can-type lithium secondary battery, a casing is generally formed of a metal, such as aluminum, and has a cylindrical shape, a prismatic shape, or a pillar shape that has rounded corners. An opening is formed in a top surface of the can, the electrode assembly is inserted into the can through the opening, and then an electrolyte is injected therein. After that, the can is covered with a cap assembly having a size and shape corresponding to the opening formed in the top surface of the can, thereby forming a sealed bare cell.
In the pouch-type lithium secondary battery, an electrode assembly is accommodated in a bottom portion of a pouch-type casing, which has a space for accommodating the electrode assembly. After that, the bottom portion is covered with a top portion of the pouch casing, sealing parts formed at edges of the top and bottom portions of the pouch casing are adhered, thereby forming a sealed bare cell.
The bare cell is electrically connected with a protection circuit board, which includes a protection element to prevent an overcharge, an overdischarge, and/or an overcurrent. In general, the bare cell and the protection circuit board are electrically connected with each other, using a lead terminal, which forms a core pack. A battery pack is completed by packing the core pack in a separate outer case, or filling a gap with a hot-melt resin, and then tubing and labeling the resultant structure, with a thin casing.
In the pouch-type secondary battery, the electrical contact between the bare cell and the protection circuit board is formed, by connecting two electrode tabs projecting from the pouch casing, with corresponding electrical terminals of the protection circuit board. The electrode tab and the protection circuit board have to be precisely combined, to prevent the electrode tabs from being bent and short-circuited, or to be connected with different electrical terminals, through another conductor.
To this end, a holder may be included between the bare cell and the protection circuit board. The holder and the protection circuit board are shaped such that the protection circuit board can be safely placed, and the gap between the bare cell and the protection circuit board can be maintained.
After that, an outer case to protect the surface of the bare cell, which is formed of stainless steel, is disposed at a side surface of the bare cell. The outer case has a resin molding part, which is formed in the gap between the bare cell and the protection circuit board. The resin molding part can be formed from a hot-melt resin that is filled into the gap.
However, when an external pressure is applied toward the gap between the bare cell and the holder, in which the protection circuit board is placed, the protection circuit board may be displaced toward the gap, thereby generating visual defects in the battery pack. Further, the contacts between the electrode tabs and the electrical terminals may be disconnected, due to the displacement of the protection circuit board, and thus, a short circuit may occur.